Momentary switch control

ABSTRACT

A portable, double insulated sharpener for drill bits or the like including a stand-up housing having a sharpening wheel driven by an electrically-operated motor. A manually-operable switch actuator is in an optimum position for one-hand actuation and control to energize the motor and sharpening wheel, while the user&#39;&#39;s other hand is free to hold the drill bit in position. Structure is provided for normally urging the switch to an &#39;&#39;&#39;&#39;off&#39;&#39;&#39;&#39; position so that when manual operation of the switch is terminated, positive control of the sharpener is achieved. This affords the user a substantial degree of control over the amount of material being removed when dressing a tool bit or the like.

United States Patent 11 1 1111 3,769,757 Sunday, Jr. 1 Nov. 6, 1973 [5 MOMENTARY SWITCH CONTROL 3,052,068 9/1962 Burgess 51 102 x 2,793,473 5/l957 Hickman... 5l/73 R X [75] lnvemor- Gauge Sunday Baltlmore, 2,914,030 11/1959 Behrens.... 51 73 R x 2,851,009 9/1958 Branvold 51 73 R x [73] Assignee: The Black and Decker M n f t i Company, Towson Primary ExammerDonald G. Kelly Attorney-Leonard Bloom et al.

[22] Filed: June 1, 1972 ABSTRACT PP N013 2581662 A portable, double insulated sharpener for drill bits or the like including a stand-up housing having a sharpen- [52] CL 51/102, 51/73 R, 51,1345 R ing wheel driven by an electrically-operated motor. A 51/17() manually-operable switch actuator is in an optimum 51 Int Cl 24, 19 1 1324 3 2 241 47 00 position for one-hand actuation and control to energize [58] Field of Search 51/73 R, 102, 12s, the motor and Sharpening wheel, While the users other 51/1345 R 166 170 R, 170 PT, 170 T 173, hand is free to hold the drill bit in position. Structure 218 219 R is provided for normally urging the switch to an off position so that when manual operation of the switch [56] References Cited is terminated, positive control of the sharpener is UNITED STATES PATENTS achieved. This affords the user a substantial degree of control over the amount ofmaterial being removed :3; 51/51 gfi when dressing a 1001 bit or the like. 311593912 12/1964 Posener 51/128 X 10 Claims, 6 Drawing Figures 1-" llll l 11" W" 1 l 13 1 .x 5 I08 1 x40 PAIENTEU NllV 6 I975 SHEET 16F 2 PMFNIED NOV 6 I975 SHEET 2 BF 2 MOMENTARY SWITCH CONTROL CROSS REFERENCES TO RELATED APPLICATIONS This application comprises an improvement related to copending application Ser. No. 76,693, filed on Sept. 30, 1970 by Henry J. Stielper and titled Double Insulated Drill Bit Sharpener, now U.S. Pat. No. 3,694,967 and that of S. G. Enders, Ser. No. 17,109, filed Mar. 6, 1970, both having an assignee common to the present application.

BACKGROUND OF THE INVENTION In conventional bench grinders for manually dressing or sharpening tools, drill bits, knives and the like, the operator applies the tool being ground and sharpened to a continuously rotating wheel. However, in the sharpener referred to in the copending applications identified above, the bit is inserted into an adjusted, accommodating aperture of the sharpener head after determining the approximate amount of relief to be formed behind the cutting edge. Then, with the bit edge to be sharpened held against the sharpening wheel, the motor is energized for a limited time, and then deenergized. The portable sharpener may be stabilized by one hand of the operator, which hand also is used to energize the switch, while the other hand is used to hold the bit. The condition of the bits being restored may vary, and a considerable range of sizes of bits can be sharpened, i. e., they range from a relatively small diameter through large sizes, from one-eighth through three-eighths inches, for example. Accordingly, the amount of material to be removed during sharpening varies. Tool sharpening requires judgement and a trialand-error procedure, and to prevent the waste of tool steel, inadvertent burning.' of the metal causing loss,

of temper and early dullness, etc., careful concentration and control during sharpening are essential.

In order to assist the user of the sharpener apparatus and afford substantially immediate cessation of grinding, it is important that the operator have substantially immediate control of the operation of the grinding wheel. Thus, once a sufficient amount of material has been removed, or thebit has been in contact with the grinding wheel over a certain period (to avoid burning"), grinding should substantially immediately cease.

FIELD OF THE INVENTION The invention resides in a portable grinder or sharpener and control switch combination permitting momentary operation or grinding and subsequent cessation of grinding to prevent buming and to assist the operator so as to remove only the desired amount of carbon or high-speed steel from the tool.

SUMMARY OF THE INVENTION The present invention is directed to portable electrically-powered sharpeners in which the grinding wheel is momentarily operated .by an electric motor controlled by a manually operated switch normally urged to an "off position and which is switched on through the application of manual pressure after the bit or other tool to be ground is oriented and hand-held in the apparatus; the release of manual pressure initiallyv actuating the switch substantially immediately causing the grounding wheel to cease being power driven whereby even though the bit or tool still engages the grinding wheel, the wheel no longer functions to grind or remove material; serving as a safety factor to obviate burning of the bit; the burning of the cutting edge of tool bits being a considerable factor in the lift-use of tool bits, avoiding unnecessary expense of replacement, continual sharpening, failure of the bits to function to accurately drill the size hold 'intended,as well as an unnecessary wear of the power tool with which i the drill bit is used. A sharp drill bit minimizes the amount of energy required to rotate it and permits the drill to function as designed.

More particularly, the primary objects of the invention are to provide in a portable, electrically-powered sharpener a fail-safe control switch mechanism affording substantially immediate positive control over the amount of material being removed during a grinding operation; to provide a double-insulated actuator for a switch mechanism normally urged to an off position; to provide a switch-operator in which cessation of manual pressure by the user de-energizes the poweroperation of a grinding wheel whereby maximum control is attained; to afford one-hand control and holding of the portable sharpener permitting the other hand to insert and hold the bit being sharpened; to provide a switch actuated in the same direction which the bit being sharpened is inserted in the sharpener and in which release of actuating pressure results in automatic de-energizing of an operating motor; to provide a double insulated switch-actuator at an optimum position on a portable sharpener casing.

Other objects and the nature and advantages of the invention will become apparent from a consideration of a detailed description of an exemplary embodiment when taken in conjunction with the drawing forming a part thereof, iin which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view partly in elevation and partly in section, showing a portable drill sharpener assembly embodying the present invention;

FIG. 2 is a top plan view of FIG. 1 with a portion 0 theupper insulating housing removed to show switchoperator support details;

FIG. 3 is a fragmentary perspective .view lookinginto the lower part of the insulating casing, showing switch and switch-actuator support details;

FIG. 4A and 4B are exploded views showing the switch utilized in the present invention in the on" and off positions; 1

FIG. 5 is an enlarged sectional view of the structure of FIG. 4B taken along the line 5-5 thereof; and

FIG. 6 isan exploded perspective view of the structure of FIG. 4A. l

Referring more specifically to the drawings, a drill sharpener embodying the present invention is illustrated generally at 11 in FIG. 1 and includes a functionally insulated motor housing 13 enclosing an electric motor 14. The motor housing 13 is disposed within a pair of telescoped insulating members 15, 16 which together form an insulating casing for the motor housing 13, the casing 16 having a flat bottom 20 for resting on a flat supporting surface. The motor housing 13 is seated within an insulating baffle 17 fixed to the casing member 16 by screws or the like, and has an end bell 26 which bottoms against ribs 19 formed on the casing member 16 and rests against a pad 21. The details of this construction along with the remainder of the construction interconnecting the casings 15, 16, the baffle 17, and the motor housing 13, do not form a part of the present invention, and are not described further here. Reference may be made, however, to the copending Stielper application identified above for a better understanding thereof.

Electric power for the motor 14 is supplied from a source through a line cord 35 which extends into the casing member 16 and is supported by a strain relief 34. The line cord 35 includes a pair of conductors 36, 38

which are connected to a slider switch 37 and the motor 14. Another conductor 32 connects the slider switch 37 to the motor 14. Another slider 39, constructed of an electrically insulating material, is interconnected with the slider 37 and has a finger portion 40 disposed exteriorly of the casing member '16 for operator control of the motor 14.

Casing member 15 does not enclose and slider 39 does not engage any live electric parts and may be made from relatively inexpensive electrically insulating material such as, for example, Acrylonitrile-Butadiene- Styrene (ABS). CYCOLAC manufactured by Marbon Chemical, Division of Borg-Warner Corp., is a suitable material. The casing member 16 and the baffle 17 enclose live electric parts and for double insulation purposes, are formed from an electrically insulating, self-extinguishing, relatively high temperature resistant material such as, for example, a 6 phenylene oxide. NORYL," manufactured by General Electric Company, is one example. Thus, the conductors 32, 36 are disposed in a way defined by a dependent skirt 46 and a plurality of lugs 50 along one side of the baffle 17,

and a plurality of upstanding lugs 48 on the casing member 16 (see FIG. 3). The conductor 38 is disposed in a way defined by a dependent skirt 44 and a lug 52 along the other side of the baffle 17, and an upstanding lug 54 on the casing 16. This construction insures that the conductors 32, 36, 38 cannot reach any of several air inlet slots 56 in the casing member 16 should these conductors break any where along their length. The

spaced arrangement of the lugs 48, and the relatively small lugs 52, 54, allows adequate cooling air to flow around skirts 46, 44 and circulate into motor housing 13. i 1

A drill bit sharpener head 42 includes a cast metal body 41 removably secured to the insulating casing member 15 by screws (not shown). An abrasive grinding wheel 45 is rotatably supported within the body 41 and is driven by and insulated from the motor 14. by means, for example, as described in the copending- Stielper application. The body 41 has a plurality of tapered, generally parallel openings 53 of different sizes formed therethrough which align with a conical sharpening surface of the wheel 45. In use, a drill bit 54 to be sharpened is inserted through a suitably sized opening 53 and pressed against the surface 55 of rotating wheel 45.

The drill bits 54 are angularly located for proper sharpening in the openings 53 by means of a plate 57 which has apertures generally aligned with openings 53 and shaped to engage at least one of the flutes in'the drill bits. This plate 57 may be angularly adjustable about the axis of the wheel 45 by means of aneccentric knob 59 rotatably supported upon the body 41. However, this construction forms no part of the invention and is not described further here. For a detailed explanation thereof, reference may be made, however, to the copending Stielper and Enders applications identified herein.

It will be appreciated that since the grinding wheel 45 is electrically insulated from the motor 14, and since the casing member 15, 16, baffle 17, and slider 39 are all constructed of non-conductive material, the entire sharpender 11 is double insulated and safe to the operator even if the functional insulation in the motor 14 and housing 13 breaks down. The structure and function described above is that of copending Stielper application, which has an assignee common to the present application.

The casing member 16 has in its upper edge a notch permitting vertical reciprocation of the switchoperating slider 39 via the finger portion 40, and the notch 100 is closed by the overlying insulating baffle plate 17 when the sharpener is assembled. Paralleling the notch 100 and depending therebelow are opposed guide ribs 101, 102 which reciprocably receive the slider 39. Immediately behind and between the guide ribs 101, 102 is a lower abutment 104 having a camming edge 106 engaging a lower end 103 of the switch housing and urging it forwardly. The insulating baffle 17 has depending from its lower surface a tubular support 107 having a downwardly-opening slot or bore 108 receiving a correspondingly shaped portion of the switch housing 105. In this manner, the switch 37 is retained and oriented in its operative position, but is readily installed, removed and replaced during assembly and/or replacement.

The switch 37 includes a metal casing 105 and cover plate 121, and has a slider block 109 disposed therein. The cover plate 121 and slider block 109 are constructed of electrically insulating material, for example, ZYTEL, manufactured by DuPont, and plate 121 is provided with spaced electric contacts 112, 1 13 having outwardly projecting terminals 123, 125 connected to conductors 32, 36, respectively, while the block 109 carries a headed metal contactor button 127 normally biased toward the contacts 112,113by a' spring 129.

The block 109' also has an operator projecting for-- wardly through an elongated opening 131 in the casing 105 and is received in a correspondingly sized aperture 133 in the slider 39. Thus, movement of the slider 39, by means of the finger portion 40, causes corresponding movement of slider block 109.

A coil compression spring 111 carried in the casing 105 normally biases the slider block 109 in an upward direction, as seen in FIGS. 4-6. Movement of the slider block 109-is limited by the size of the opening 131 in casing 105, and in the normal, upward position of slider block 109, shown in FIGS. 4A and 6, contactor button 127 engages only contact 112 so that the circuit to motor 14 is open when the slider block 109 is moved downwardly, against the force of spring 111, button 127 engages both contacts 112, 113 (FIGS. 48 and 5) and closes the motor circuit. This is achieved by pushing downwardly on finger portion 40 of slider 39. When finger portion 40 is released, spring 111 opens the switch 37. It will be understood that a spring engaging the slider 39 could be substituted for the spring 11 1. As described above, the slider block 109 and slider 39 are produced from a suitable electrically insulating plastic (of character mentioned) which serves to prevent shocks to the person operating the sharpener. The spring means 111 via the slider block 109 and operator 110 normally urges the slider 39 and its finger portion 40 upwardly and is overcome by manual pressure applied by the users thumb 115 as illustrated in FIG. 1. The plastic used to form the various electrically insulating parts mentioned above also functions as a relatively smooth bearing surface minimizing resistance to ready actuation and return to a switch-open condition at slider 39 as illustrated in FIG. 1, and normally maintained by the return spring means 111.

When sharpening drill bits, the amount of material removed to re-establish the proper cutting edge is relatively small; and just as important as a sharp leading cutting edge on the fluted drill bit is the relief behind the cutting edge. As has been mentioned above, the sharpener of the present invention incorporates plate 57 and control 59 assisting the user of the tool to develop the proper relief behind the leading cutting edge. Since both cutting edges of the drill bit must be sharpened, user-judgement plays an important part when sharpening or dressing the bit. In order to assist the person operating the sharpener, the permit ready removal of pressure on the finger engagable portion 40, while the bit is held in engagement with the abrasive grinding wheel 49, the switch means causes substantially instantaneous cessation of the electric motor 14 and grinding ceases. The motor operates for a relatively small period, continued application of the bit on the wheel does not result in continued grinding and, just as important, heating of the tempered tool steel of the bit is stopped. Since the leading cutting edge of the bit (or a sharpened edge of any tool) is a relatively thin fine line, and since a thin edge is more susceptible to overheating than a relatively thick section, overheating or burning of this edge is avoided so that critical, loss-oftemper temperatures are not exceeded or maintained over a long period.

Accordingly, means are provided whereby the user of the sharpener has relatively finite control over the duration of grinding pressure and/or generation of heat.

Preferably the finger portion 40 is actuated toward the downward position when closing the switch 37', arid this is the same direction the drill bit 54 is inserted into the sharpener. However, the switch actuationcould be in other directions without departing from the spirit and intent of the invention. Likewise, although the preferred embodiment has received unusual success and acceptance, switch actuators having similarly'functioning mechanical equivalents are within the purviewv of the invention.

The finger portion 40,'it will be noted, is located adjacent the side edge of member 15 whereby a users thumb 115 is oriented into a natural position when grasping the member 15 in the span of the users hand to stabilize the sharpener 1 l. The users other hand 1 16 is free to insert the drill bit 54 into the accommodating opening 53. The location of the element 40 permits, after relatively short period of use of the sharpener, operation of the sharpener motor with maximum concentration on the drill bit being sharpened; further, the thumb 115 is readily slipped off the element 40 resulting in de-energization of the motor. Since the tool is a portable one, the spanning of ones hand about the member 15 affords manual stability permitting the sharpener to be readily operated and controlled. In the event the grinding wheel 45 or bit 54 becomes jammed,

removal of actuating pressure on element 40 results in immediate opening of switch 37 to obviate overloading or burning out of the motor windings, insulation, etc. Further, in addition to the multiple-electrical insulating features afforded by the housing parts 15, 16 and the baffle 17, additional electrically-insulating is afforded by the plastic slider 39 Of course, chips, grindings, etc. are enclosed in the housing 41 and the danger of flying chips or grindings is minimized, although the usual safety precautions accompanying the use of such tools with moving parts and electric motors is recommended.

Through the foregoing, there has been disclosed a novel insulated, momentary control switch construction which in addition to the safety features in the disclosed combination, affords means facilitating finite control of sharpening and means to avoid burning of the critical tool cutting edge being dressed.'While a preferred form of the invention has been illustrated and described in detail, clearly fulfilling the inventive ob- 20 jects set forth, various additions, substitutions, modifications and omissions may be made thereto without departing from the spirit of the invention.

I claim: Y I

1. A portable sharpener for drill bits'or the like including a casing having a relatively flat base for resting on a supporting surface, electrically-operated power means supported within said casing and including grinding means operatively connected thereto, means guidably receiving said drill bit and including means engageable therewith to angularly position said drill bit for proper sharpening engagement with said grinding means, switch means operatively connected to said power means and normally biased toward an of position, said switch means including a manuallyengageable actuator portion accessibly disposed exteriorly of said casing for momentary manual engagement and movement by a user of the sharpener to turn said drill bit for proper sharpening engagement with said grinding means, and normally open switch means operatively connected tosaid motor means, said switch means including a manually engageable actuator element accessible exteriorly of said casing for movement by a user'in one direction for closing said'switch means,

said switch means including means normally urging saidswitch means to an off position whereby the motor means can be momentarily activated.

3. A portable sharpener as defined in claim 2, in

which said casing includes electrically insulating means for holding said switch means in an operative position and permitting ready installation andremoval.

4. A portable sharpener as defined in claim 2, in which said actuator element comprises an independent, electrically-insulating element displaceably supported on said casing and operatively connected to said switch means. 1 4

5. A portable sharpener as defined in claim 4,- in which said casing is constructed from an electricallyinsulating material, said casing including means guidingly engaging said independent element and positioning it during its path of movement during manual actuation.

6. A portable sharpener as defined in claim 2, in which said actuator element comprises a separate, electrically-insulating element operatively connected to said switch assembly and normally urged in one direction by the switch assembly, and the means for urging the switch means to an off position.

7. A portable sharpener for drill bits or the like, including a casing, electrically-operated power means supported within said casing and including grinding means operatively connected thereto, normally open switch means operatively connected to said power means and including a manually-engageable actuator portion accessibly disposed exteriorally of said casing for momentary manual engagement by a user of the sharpener to close a circuit to energize the electric motor means, said casing comprising an electrically insulating material, an electrically insulating baffle including means for orienting the power means, said baffle means including a depending switch mounting-andorienting portion for positioning the switch means in operative relation, said casing including a portion orienting said switch means in an operative position in the lower portion of said casing, said switch means including a separate, electrically-insulating displaceable actuator element including said manually-engageable actuator portion, said displaceable actuator portion being mechanically connected to said switch means whereby movement thereof is immediately reflected by corresponding operation of said switch means.

8. A portable sharpener as defined in claim 7, in which said casing includes rib portions guidingly engaging said displaceable actuator element for movement therealong during operation of said switch means.

9. A portable sharpener for drill bits or the like, in-

cluding a casing, electrically-operated power means supported within said casing including grinding means operatively connected thereto, means guidably receiving said drill bit and including means engageable therewith to angularly position said drill bit for proper sharpening engagement with said grinding means, switch means operatively connected to said power means and normally biased toward an of position, said switch means including a manually-engageable actuator portion accessibly disposed exteriorly of said casing for momentary manual engagement and movement by a user of the sharpener to turn said switch means on to energize the electric motormeans, said switch means returning to said off position immediately upon release of said actuator portion, said casing being of a size and shape to be grasped at its lower portion within the span of a user's hand, said manually-engageable actuator portion being exposed adjacent the lower portion of the casing for ready, momentary engagement by at least a portion of a users hand while grasping the housing whereby the users other hand is free to apply the drill bit being ground.

10. A portable sharpener for drill bits or the like, including a casing, electrically-operated power means supported within said casing and including grinding means operatively connected thereto, means guidably receiving said drill bit and including means engageable therewith to angularly position said drill bit for proper sharpening engagement with said grinding means, switch means operatively connected to said power means and normally biased toward an off position, said switch means including a manually-engageable actuator portion accessibly disposed exteriorly of said casing for momentary manual engagement and movement by a user of the sharpener to turn said switch means on to energize the electric motor means, said switch means returning to said off position immediately upon release of said actuator portion, said casing including means electrically insulating said power means from said casing and said grinding means, means electrically insulating said switch means from said power means and said casing, said manuallyengageable actuator portion comprising a separate, electrically-insulating element displaceably supported on said casing whereby movement thereof reflects operation of said power means. 

1. A portable sharpener for drill bits or the like including a casing having a relatively flat base for resting on a supporting surface, electrically-operated power means supported within said casing and including grinding means operatively connected thereto, meaNs guidably receiving said drill bit and including means engageable therewith to angularly position said drill bit for proper sharpening engagement with said grinding means, switch means operatively connected to said power means and normally biased toward an ''''off'''' position, said switch means including a manually-engageable actuator portion accessibly disposed exteriorly of said casing for momentary manual engagement and movement by a user of the sharpener to turn said switch means ''''on'''' and energize the electric motor means, said switch means returning to said ''''off'''' position immediately upon release of said actuator portion.
 2. A portable drill bit sharpener apparatus, including a casing, electrically-operated power means supported within said casing, abrasive sharpening wheel means operatively connected to said motor means for engagement with the portion of a drill bit to be sharpened, means guidably receiving said drill bit and including means engageable therewith to angularly position said drill bit for proper sharpening engagement with said grinding means, and normally open switch means operatively connected to said motor means, said switch means including a manually engageable actuator element accessible exteriorly of said casing for movement by a user in one direction for closing said switch means, said switch means including means normally urging said switch means to an ''''off'''' position whereby the motor means can be momentarily activated.
 3. A portable sharpener as defined in claim 2, in which said casing includes electrically-insulating means for holding said switch means in an operative position and permitting ready installation and removal.
 4. A portable sharpener as defined in claim 2, in which said actuator element comprises an independent, electrically-insulating element displaceably supported on said casing and operatively connected to said switch means.
 5. A portable sharpener as defined in claim 4, in which said casing is constructed from an electrically-insulating material, said casing including means guidingly engaging said independent element and positioning it during its path of movement during manual actuation.
 6. A portable sharpener as defined in claim 2, in which said actuator element comprises a separate, electrically-insulating element operatively connected to said switch assembly and normally urged in one direction by the switch assembly and the means for urging the switch means to an ''''off'''' position.
 7. A portable sharpener for drill bits or the like, including a casing, electrically-operated power means supported within said casing and including grinding means operatively connected thereto, normally open switch means operatively connected to said power means and including a manually-engageable actuator portion accessibly disposed exteriorally of said casing for momentary manual engagement by a user of the sharpener to close a circuit to energize the electric motor means, said casing comprising an electrically insulating material, an electrically insulating baffle including means for orienting the power means, said baffle means including a depending switch mounting-and-orienting portion for positioning the switch means in operative relation, said casing including a portion orienting said switch means in an operative position in the lower portion of said casing, said switch means including a separate, electrically-insulating displaceable actuator element including said manually-engageable actuator portion, said displaceable actuator portion being mechanically connected to said switch means whereby movement thereof is immediately reflected by corresponding operation of said switch means.
 8. A portable sharpener as defined in claim 7, in which said casing includes rib portions guidingly engaging said displaceable actuator element for movement therealong during operation of said switch means.
 9. A portable sharpener for drill bits or the like, including a casing, electrically-operated power means supported within said casing including grinding means operatively connected thereto, means guidably receiving said drill bit and including means engageable therewith to angularly position said drill bit for proper sharpening engagement with said grinding means, switch means operatively connected to said power means and normally biased toward an ''''off'''' position, said switch means including a manually-engageable actuator portion accessibly disposed exteriorly of said casing for momentary manual engagement and movement by a user of the sharpener to turn said switch means ''''on'''' to energize the electric motor means, said switch means returning to said ''''off'''' position immediately upon release of said actuator portion, said casing being of a size and shape to be grasped at its lower portion within the span of a user''s hand, said manually-engageable actuator portion being exposed adjacent the lower portion of the casing for ready, momentary engagement by at least a portion of a user''s hand while grasping the housing whereby the user''s other hand is free to apply the drill bit being ground.
 10. A portable sharpener for drill bits or the like, including a casing, electrically-operated power means supported within said casing and including grinding means operatively connected thereto, means guidably receiving said drill bit and including means engageable therewith to angularly position said drill bit for proper sharpening engagement with said grinding means, switch means operatively connected to said power means and normally biased toward an ''''off'''' position, said switch means including a manually-engageable actuator portion accessibly disposed exteriorly of said casing for momentary manual engagement and movement by a user of the sharpener to turn said switch means ''''on'''' to energize the electric motor means, said switch means returning to said ''''off'''' position immediately upon release of said actuator portion, said casing including means electrically insulating said power means from said casing and said grinding means, means electrically insulating said switch means from said power means and said casing, said manually-engageable actuator portion comprising a separate, electrically-insulating element displaceably supported on said casing whereby movement thereof reflects operation of said power means. 